The invention relates to a motor pump unit for a high-pressure cleaning apparatus having an electric motor and a pump, wherein the electric motor comprises a motor housing that is surrounded by a cooling housing with an annular space having an annular space inlet and an annular space outlet formed therebetween, and wherein the pump has a drive housing on which is supported a motor shaft of an electric motor, and has a suction inlet for drawing in liquid and a pressure outlet for discharging pressurized liquid, wherein the annular space outlet is fluidly connected to the suction inlet and wherein liquid to be pressurized by the pump can be supplied to the annular space inlet.
A motor pump unit of this type is known from DE 10 2007 009 394 A1. It is used in a high-pressure cleaning apparatus by means of which a liquid, preferably water, can be supplied to a pump space via the suction inlet, pressurized and then discharged via the pressure outlet. The pressure outlet can have connected to it a pressure hose which may, for example, have a spray lance arranged at its free end, so that pressurized liquid can, for example, be directed towards an object to be cleaned.
The pump is driven by an electric motor which can be cooled by the liquid that is supplied to the suction inlet of the pump. To this end, the motor housing is surrounded by a cooling housing, wherein an annular space having an annular space inlet and an annular space outlet is formed between the cooling housing and the motor housing. The liquid to be pressurized by the pump can first be supplied to the annular space inlet, then flow through the annular space and subsequently be supplied to the suction inlet by way of the annular space outlet. It is thus possible to dispense with additional air cooling as is often provided in electric motors. Instead, the waste heat from the electric motor is dissipated to the liquid to be pressurized by the pump. This has the advantage of making the motor pump unit suitable for being inserted in a splash-proof housing of the high-pressure cleaning apparatus without having to provide inlet and outlet air openings in the housing of the high-pressure cleaning apparatus.
However, during operation of the motor pump unit, not only does the electric motor heat up but also the drive housing of the pump experiences considerable heat load. One reason for this is that the motor shaft is supported on the drive housing.